Known wheeled arrangements, eg conventional wheelchairs, generally encounter difficulties in climbing obstacles such as steps, curbs etc. This is because a wheel is generally only able to climb a step with a height of at most 1/4 to 1/3 the diameter of the wheel, the actual step height climbable also depending on other factors such as the magnitude of the driving force applied. Wheelchairs typically have a pair of small wheels, so their climbing capabilities are generally fairly limited, restricting the terrain and circumstances in which they can be used.